The present invention relates to a process for the low temperature sintering of ceramic materials that have been infiltrated by an inorganic polymer. The process provides ultra smooth ceramic materials useful in the electronics industry.
As integrated circuit technology has developed over the past several decades, certain materials have been preferred in the production of substrates for mounting or carrying the semiconductor chips in which complex, densely packed circuitry is embedded. In particular, because of their exceptional insulating properties, ceramics and glass ceramics have become the most preferred materials for the substrates. However, in order to serve the purposes described, the substrates constituting this material are required to have a high degree of flatness, and also to posses a high quality smooth surface.
The surface roughness of substrates to be used in the electronics industry is typically measured by the centerline average roughness (CLA). The CLA is directly proportional to the diameter of the grains that make up the sintered body of a ceramic material. AS the diameter of the grain size increases so does the surface roughness of the ceramic substrate. The grain size of the ceramic material is primarily determined by two factors, first the size of the ceramic particles, and second, the temperature at which the ceramic material is sintered.
One method of trying to decrease the surface roughness of the ceramic material is to use smaller sized ceramic particles. The use of the smaller ceramic particles results in the sintered material grain size being smaller compared to when larger ceramic particles are used. However, the problem that is encountered by using the smaller size ceramic particles involves the difficulty in handling such particles. The small particles are essentially a powder that is difficult to disperse and form into a green compact of ceramic material prior to sintering.
The grain size of the sintered ceramic material is also determined by the temperature that the sintering occurs. As the temperature that the sintering occurs increases, the grain growth is promoted. Therefore, it would be desirable to decrease the temperature that the sintering is carried out. The problem with this approach is that the minimum sintering temperature is determined by the size of the voids present in the green compact of ceramic material. In order to decease the minimum sintering temperature, it is necessary to decrease the size of the voids in the green compact of ceramic material. This reduction in the size of the voids may be achieved by using smaller sized ceramic particles, however, this again suffers from the drawback discussed above with regard to small size particles.
U.S. Pat. No. 4,369,154 to Dougherty relates to a method for preparing smooth ceramic substrates useful in the electronics industry. Such substrates are prepared from ceramic compacts comprising alumina or glass ceramic, an organic bonding agent, a plasticizing agent, an emulsifying agent, a glass frit and a solvent. The composition is consolidated and formed into a compact that is lapped prior to the sintering step at conventional temperatures.
Therefore, it is an object of the present invention to provide an efficient method for preparing ultra smooth surface ceramic materials that may be used in the electronics industry.
It is another object of the present invention to provide a method of preparing such ultra smooth ceramic materials by using a low temperature sintering process.